The present invention pertains generally to tire pressure sensor devices, and more particularly, to a method and apparatus for remotely sensing the pressure of a tire by monitoring a tire parameter that is indicative of the pressure of a tire.
Premature wear of a tire is due to under- and/or over-inflation. Under-inflation wears the side edges of the tire footprint; over-inflation wears the middle of the tire footprint.
Tire temperature is critical for tire integrity. Tire temperature is a function of tire pressure,. weight load, rotational speed, and outside temperature, among other factors such as tire construction. A tire is temperature rated and is designed to rotate below the rated maximum temperature and speed. As the speed of rotation of the tire increases, the repetition rate of flexure increases, thereby causing the temperature of the tire to increase. The potential of tire failure (i.e., xe2x80x9cblow outxe2x80x9d) increases when the maximum rated safe temperature is exceeded.
Prior art techniques and devices for monitoring tire temperature and pressure include systems which sense the pressure inside a tire by utilizing a pressure sensor located within the tire itself. A difficulty in implementing such a system is determining how to communicate the output of the pressure sensor located within the rotating tire to a warning display typically located in a fixed position on the vehicle""s dashboard.
One example of such a system is described in U.S. Pat. No. 5,285,189, which teaches a tire pressure monitoring system that utilizes radio frequency (RF) signals transmitted from transmitters located within the tires to a dedicated external receiver. In this system, the transmitter includes a microcontroller coupled to a pressure sensor located within the tire for generating and transmitting encoded radio signals at the same carrier frequency. The encoded radio signals include tire pressure information and transmitter device identification information, which is useful for identifying from which tire the tire pressure information is transmitted. A receiver located on the block of the vehicle receives the encoded radio signal and decodes the transmitted information to provide the vehicle operator an alarm if low tire pressure is detected. One problem with this system is the excessive implementation cost. In addition, the placement of separate microcontrollers in the mechanically and thermally harsh environment of each tire increases the potential damage to the pressure sensors. Another problem with this system is electromagnetic interference (EMI). The radio receiver is vulnerable to noise and other interfering radio signals. Also, the transmitter in the tire can cause interference with other radio devices within the car or nearby cars.
In other prior art wireless tire temperature and pressure monitoring devices, a transceiver device is attached to the tire itself. This is problematic for two reasons. First, it requires more complicated communication. If either the transceiver in the tire or on the block of the vehicle fails, the entire system fails. Second, because a transceiver device must be mounted on the tire, the system requires cooperation between the vehicle manufacturer and the tire manufacturer. It would be desirable to eliminate the requirement for a transceiver device on the tire itself in order to allow the system to be tire manufacturer independent and to reduce the number of required components and complexity and therefore the likelihood of system failure.
Accordingly, a need exists for a new and improved technique for monitoring, measuring, and reporting tire temperature and pressure to detect out-of-rating conditions that could lead to tire failure.
The present invention is a novel technique and system that allows the pressure of a tire to be remotely monitored by sensing a tire parameter indicative of the tire""s pressure without mounting any device on the tire itself and while the tire is rotating. In the illustrative embodiment, a tire parameter indicative of the pressure inside the tire such as the temperature, acoustical signature, or shape of the tire, is measured remotely with a remotely mounted sensor. The measured parameter is compared to a range of known acceptable limits for that particular parameter, and a warning signal is generated if the measured parameter is not within that range of acceptable limits. Preferably, the measured parameter and/or the pressure, as derived from the measured parameter, is displayed in a location (e.g., the dashboard of the vehicle) convenient to the operator of the device on which the tire is mounted in order to provide visible notification.
In accordance with the invention, a parameter of a tire that is indicative of the tire pressure is remotely monitored by a remote sensor. The remote sensor measures the parameter of the tire to generate a measured parameter. The parameter measurement is monitored by a measurement processor which compares the measurement itself to a set of acceptable parameter threshold limits and generates a warning signal if measurement is not within the required limits. Alternatively, the measurement is used to derive another parameter (such as the actual tire pressure or another parameter indicative of the tire pressure), which is compared to a set of acceptable parameter threshold limits. If the derived parameter is not within the required limits, a warning signal is generated.
In a first illustrative embodiment, the remote sensor is implemented with an infrared (IR) detector which measures the temperature of the tire, from which the actual pressure is calculated or from which the tire pressure is inferred.
In a second illustrative embodiment, the remote sensor is implemented with an acoustical transducer that measures the acoustical signature of the tire. The remote sensor in this embodiment may be implemented using a variety of known sensors, including an ultrasound detector, a microphone, or an accelerometer, or any equivalent thereof.
In a third illustrative embodiment, the remote sensor is implemented with a distance detector that measures the shape of the tire, such as the width of the tire as indicated by the relative distance between the remote sensor and a predetermined point on the tire. The remote sensor in this embodiment may be implemented with a camera, an ultrasound detector, a microphone, an infrared detector, a microwave oscillator, or any known or hereinafter known equivalent thereof.
Preferably, the measurement processor receives a set of reference parameters which are used to determine whether the measured parameter is within the acceptable limits. The determination may be based only on the measured parameter itself for the conditions indicated by the set of reference parameters. Alternatively, the measured parameter may be used along with the set of reference parameters to derive either the actual tire pressure itself or yet another parameter that is indicative of the tire pressure. The measurement processor then determines whether the actual derived tire pressure or derived parameter is within the acceptable limits for the conditions.
In one embodiment, there is provided a lookup table that contains a set of reference parameter values and their corresponding threshold limits.
The invention allows the tire pressure to be monitored at any non-zero rotational speed of said tire. In addition, if the third embodiment is used, that is, where the measurement is a parameter indicative of the shape of the tire (such as the relative distance between the sensor and a predetermined point on the tire), the tire pressure can be monitored when the tire is not rotating as well.
Preferably, the tire parameter monitoring apparatus includes a trend analyzer which monitors the history of the parameter measurements from which it is able to detect trends (e.g., increasing tire temperature, yet still within the acceptable threshold limits), and generates a trend indicator when a trend is detected.